Heat sink



FIG. 1 is a perspective view of a heat sink;

FIG. 2 is a front elevation thereof;

FIG. 3 is a rear elevation thereof;

FIG. 4 is a left side elevation thereof;

FIG. 5 is a right side elevation thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom view thereof. 

The ornamental design for a heat sink, as shown and described. 